Advances to Money Pool

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- Definition

Borrowings from Money Pool

+ References

No definition available.

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- Definition

Amount of debt and equity financial instruments classified as either held-to-maturity or available-for-sale.

+ References

No definition available.

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- Definition

Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
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- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

This item represents disclosure of all significant concentrations of credit risk or market risk arising from the subject financial instrument (as defined), whether from an individual counterparty or groups of counterparties.

+ References

No definition available.

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- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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- Definition

Amount of long-term debt and capital lease obligation due after one year or beyond the normal operating cycle, if longer.

+ References

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- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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- Definition

Value of all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by shareholders, which is net of related treasury stock. May be all or a portion of the number of preferred shares authorized. These shares represent the ownership interest of the preferred shareholders.

+ References

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- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(19)(a))
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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of short-term debt existing as of the balance sheet date.

+ References

No definition available.

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Fair Value Measurements (Schedule Of Carrying Amounts And Estimated Fair Values Of Financial Assets and Liabilities) (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt	$ 506	$ 484
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	96	68	$ 53	$ 52
Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt	0	39
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	25	7	5	5
Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt	0	62
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	57	41	$ 28	$ 28
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt	506	484
Long-term debt (including current portion)	8,460	7,935
Preferred stock	142	142
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	96	68
Debt Issuance Costs, Net	56	50
Carrying Amount \| Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Advances to Money Pool	66
Available-for-sale Securities and Held-to-maturity Securities	276	276
Short-term Debt		39
Long-term debt (including current portion)	4,202	3,961
Preferred stock	80	80
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	25	7
Debt Issuance Costs, Net	23	20
Carrying Amount \| Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Borrowings from Money Pool	31
Short-term Debt		62
Long-term debt (including current portion)	3,113	2,830
Preferred stock	62	62
Fair Value, Concentration of Risk, Cash and Cash Equivalents	57
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents		41
Debt Issuance Costs, Net	27	24
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	506	484
Investments, Fair Value Disclosure	276	276
Long-term Debt, Fair Value	8,849	8,531
Preferred stock	140	131
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	96	68
Fair Value \| Quoted Prices In Active Markets For Identical Assets or Liabilities (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	0	0
Investments, Fair Value Disclosure	0	0
Long-term Debt, Fair Value	0	0
Preferred stock	0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	96	68
Fair Value \| Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	506	484
Investments, Fair Value Disclosure	276	276
Long-term Debt, Fair Value	8,411	8,531
Preferred stock	140	131
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	0
Fair Value \| Significant Other Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	0	0
Investments, Fair Value Disclosure	0	0
Long-term Debt, Fair Value	438	0
Preferred stock	0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	0
Fair Value \| Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Advances to Money Pool	66
Short-term Debt, Fair Value		39
Investments, Fair Value Disclosure	276	276
Long-term Debt, Fair Value	4,544	4,348
Preferred stock	79	80
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	25	7
Fair Value \| Union Electric Company \| Quoted Prices In Active Markets For Identical Assets or Liabilities (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Advances to Money Pool	0
Short-term Debt, Fair Value		0
Investments, Fair Value Disclosure	0	0
Long-term Debt, Fair Value	0	0
Preferred stock	0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	25	7
Fair Value \| Union Electric Company \| Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Advances to Money Pool	66
Short-term Debt, Fair Value		39
Investments, Fair Value Disclosure	276	276
Long-term Debt, Fair Value	4,544	4,348
Preferred stock	79	80
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	0
Fair Value \| Union Electric Company \| Significant Other Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Advances to Money Pool	0
Short-term Debt, Fair Value		0
Investments, Fair Value Disclosure	0	0
Long-term Debt, Fair Value	0	0
Preferred stock	0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	0
Fair Value \| Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value		62
Borrowings from Money Pool	31
Long-term Debt, Fair Value	3,187	3,028
Preferred stock	61	51
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	57	41
Fair Value \| Ameren Illinois Company \| Quoted Prices In Active Markets For Identical Assets or Liabilities (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value		0
Borrowings from Money Pool	0
Long-term Debt, Fair Value	0	0
Preferred stock	0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	57	41
Fair Value \| Ameren Illinois Company \| Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value		62
Borrowings from Money Pool	31
Long-term Debt, Fair Value	3,187	3,028
Preferred stock	61	51
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	0
Fair Value \| Ameren Illinois Company \| Significant Other Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value		0
Borrowings from Money Pool	0
Long-term Debt, Fair Value	0	0
Preferred stock	0	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 0	$ 0